Who likes going to the dentist? University of Guelph researchers are studying dogs’ mouths for bacteria that might play a role in periodontal disease, which affects an estimated eight out of 10 dogs by four years of age.

“We are learning about the kinds of bacteria in dogs’ mouths in order to help avoid dental and oral diseases,” said pathobiology graduate student Amy Sturgeon, lead author on a recent paper on the topic. “We also hope to improve our understanding of how these bacteria may cause problems for people through direct contact.”

Led by Scott Weese, a pathobiology professor in U of G’s Ontario Veterinary College, the research team aimed to learn how many kinds of bacteria live in dogs’ mouths and potential health implications both for dogs and for humans. They found more kinds of bacteria than in previous studies, thanks partly to their study method.

Weese explained: “Investigating the types and roles of the bacteria in dogs’ mouths is usually limited to cloning-based sequencing and conventional culture-based studies. We’ve known these weren’t great, but until recently we didn’t have any other options. Now we’re able to take advantage of recent advances in next-generation sequencing and bioinformatics to truly investigate complex bacterial populations like those in the dog’s mouth. We didn’t grow the bacteria in petri dishes, but extracted DNA, identified the sequences and compared them with existing bacteria DNA databases.”

By examining the DNA of oral bacteria from six healthy dogs, the researchers found that the oral population is highly complex, rivalling intestinal bacteria in diversity.

“We expected to find a number of bacterial species,” said Sturgeon. “But we were surprised at how complex and diverse the range of species was and at how many bacterial species were identified.”

The animals were clinically healthy, were fed commercial diets without raw or unpasteurized meat or milk products, and had undergone no dental cleaning, surgery, general anesthesia or antibiotic treatments within the preceding three months.

“Our results support the concept of a group of bacteria common to the oral cavity among all dogs,” said Sturgeon. “These core bacteria are probably the most important ones: species that have evolved and adapted to live with dogs. However, this core population also contained bacteria known to cause dental disease and serious infections in humans. That wasn’t surprising. We know that the mouth harbours a wide range of bacteria that can cause disease, given the right circumstances.”

The most common bacteria found were a type that is frequently involved in gingivitis. The second most abundant kind commonly causes human dental plaque.

The next step is to understand how the oral microflora influence disease, for better prevention, diagnosis and treatment.

“Hopefully, as we learn more about the prevalence of different bacteria in dogs’ mouths, we will be able to develop new ways to combat periodontal disease,” Sturgeon said. “This will go a long way towards helping our pets live happy, prolonged lives.”